Comparatively little is known about the changes that occur in the aging pulp. Still less is known about the capacity of the aging pulp to respond to injurious conditions. Our proposed research will test the hypothesis that aging pulp suffers a decline in function and an impairment of its wound healing capacity. The status of young and aged pulps will be compared with respect to the properties of the extracellular matrix (collagen and glycoaminoglycans [GAGs]) and the distribution and vitality of odontoblast phenotypes. Further, the life-long dentinogenic activity of odontoblasts will be measured by a radiographic assessment of secondary dentin formation in the teeth aging humans. The cohorts provided by the San Antonio Heart Study (SAHS) and the San Antonio Longitudinal Study of Aging (SALSA) will provide a population of aging individuals that is evenly distributed with respect to age, gender, and ethnicity. To evaluate the healing potential of aging pulp, the extent and quality of reparative dentin formation in cervically decayed or abraded human teeth will be examined. In a companion study, the reparative capacity of aging pulps will be evaluated in young and old rats in situ.. To delve more deeply into the properties of aging pulp, a number of in vitro experiments are planned. Cultures of human pulp will first be evaluated for proliferative capacity and stability of phenotypes through several passages. Basal levels of collagen and GAGs synthesis will next be established for young and aged human pulp cells in culture. As a measure of responsiveness, the capacity for reparative dentin formation by young and aged pulp will be assayed by mineralized nodule formation in specially-supplemented cultures. We will also evaluate in vitro the ability of 1,25 (OH)2D3- to evoke alkaline phosphatase activity, platelet derived growth factor (PDGF) to stimulate mitosis, acidic fibroblast growth factor (aFGF) to promote GAGs synthesis, and calcitonin gene-related peptide (CGRP) to increase collagen production. The variety of approaches proffered to evaluate the aging pulp should significantly enhance our knowledge about this neglected organ.